The statements in this section merely provide background information related to the present teachings and may not constitute prior art.
The ability to transfer water between fluid streams that are maintained separate from one another can be useful in a variety of applications. By way of example, one such application is in a fuel cell system wherein one or more of the reactant streams are humidified by another fluid stream.
Fuel cells can be operated in a manner that maintains a membrane, such as a proton exchange membrane (PEM), in a humidified state. The humidity level of the membrane can affect the performance of the fuel cells. The membrane can be damaged if operated in a dry condition which can result in immediate failure or reduction of the useful life of the fuel cells. To humidify the membrane, the fuel cells can be operated in a flooded condition during which the humidity level within the fuel cells is greater than 100% and liquid water is formed during the production of electricity.
To further humidify the membrane, the cathode and/or anode reactant gases being supplied to the fuel cells can be humidified in a water transfer device. The water transfer device can receive a cathode effluent, expelled from the fuel cells, which can contain water in a gaseous and/or liquid state. A portion of the water content of the cathode effluent can be transferred to the cathode or anode reactant gas also flowing through the water transfer device. In this manner, the humidity of the cathode or anode reactant gas can be increased before being supplied to the fuel cell.
The water transfer, or water flux, can be facilitated by a water transfer membrane assembly within the water transfer device. Traditional water transfer membrane assemblies facilitate water flux from only the gaseous portion of the water content while the liquid water portion is expelled from the water transfer device along with the associated fluid stream. Expelling liquid water can be a lost resource. Accordingly, it would be advantageous to have a water transfer device capable of utilizing liquid water to increase water flux. It would be further advantageous to increase the efficiency of the water transfer device. Increased efficiency can advantageously allow the use of a smaller water transfer device to humidify a given fluid stream. Increased efficiency can also advantageously reduce the amount of water lost (unrecovered) from the system within which the water transfer device is utilized.